(1) The Field of the Invention
This invention relates to improved adhesive compositions. More precisely, this invention relates to adhesive compositions including ethylenically unsaturated compounds, a source of free radicals and an activator comprising a pyrazoline compound.
(2) Description of the Prior Art
Many polymerizable compositions are known which are believed to cure or harden by free radical polymerization of ethylenically unsaturated components. Such components may include for example acrylic or methacrylic monomers, vinyl chloride, vinylidene chloride, vinyl acetate, styrene, itaconic acid, maleic acid, and unsaturated polyesters.
In the field of polymerizable adhesives for example, reactive fluid adhesive compositions are known which cure at room temperature by addition polymerization of monomeric components to provide adhesive bonds between surfaces of many different materials. Adhesive compositions intended to cure between opaque, impervious, or other materials to form an adhesive bond may comprise one or more polymerizable acrylate or methacrylate ester monomers, a source of free radicals such as a peroxide, hydroperoxide, per ester or per acid, and an activator for interaction with the source of free radicals to initiate polymerization of the monomers at room temperature. The source of free radicals and the activator may be stored separated from each other prior to use of the adhesive; for example one of them may be incorporated in admixture with the monomers during storage. In this way, the adhesive composition comprises two parts and the composition is cured to form an adhesive bond when the two parts are brought together in absence of oxygen.
In one particularly convenient method of using two part reactive fluid adhesives, one part of the composition comprising the activator is applied to a surface to be bonded in the manner and form of a primer. Thereafter, the other part of the composition comprising the polymerizable monomers and source of free radicals is applied to the primer coated surface. This method permits the use of the adhesive composition without the necessity of mixing the two parts to application. The activator is conveniently one which can be used in non-stoichiometric quantities with respect to the monomers.
While bonds formed from two part adhesive compositions are highly useful, certain two part compositions comprise amine-aldehyde reaction products as activators which are liquid materials having a certain degree of toxicity and offensive odor. In view of the increasing emphasis in favor of using non-toxic materials in commercial products, it is desirable to provide an adhesive composition comprising an activator system having a more acceptable level of toxicity and odor. In this context, the use of solid materials as activators may be an apparent consideration. However, the achievement of a commercially acceptable adhesive bond usually implies that bond forming materials cannot be present in the bond in solid form.
An object of the present invention is to provide an activator for use with polymerizable, room temperature curing adhesive compositions comprising ethylenically unsaturated monomeric acrylate and methacrylate esters, and to provide adhesive compositions including such activators.
Another object of the present invention is to provide an activator for use with polymerizable compositions comprising ethylenically unsaturated monomers, which activator comprises material which can be readily manufactured from relatively inexpensive raw materials.
Other objects and advantages of the present invention will be apparent from the following description of the invention and the preferred embodiments thereof.